Hydrocarbon conversion process



Feb. 15, 1938'. F. w. SULLlVAN. JR. 2,108,395

HYDROCARBON GONVERS ION PROCESS Filed Dec. 30, 1933 2 Shgets-Shect 1 Preasurelieatsr INVENTOR I fiederzck WSaZZwazzJr Fresh 0L1 ATTORNEY Feb. 15, 1938. F. w. SULLIVAN. JR

' HYDROCARBON CONVERSION PROCESS 2 Sheets-Sheet 2 Filed Dec. so 1933 W M k a M Rd W n M w .\.O\ 7 M M v 1w m an E r um m B R \Qm mu 0\ mm L Patented Feb.'- l5, 1938 UNITED STATES PATENT OFFICE" 6 Claims. "(01. 196-9) My-invention relates to an improvementin the art of hydrocarbon conversion processes or in other words, to an improved process for the conversion of hydrocarbon gas and relatively heavy hydrocarbon oils to relatively light oils of the gasoline boiling range.

The commercial development of present day oil cracking processes has been-long andcomplex but has been characterized by relatively 10 few radical changes'in the types of processes.

First were the simple bulk distillation processes wherein relatively clean virgin charging stock was introduced into a direct-fired shellstill and I distilled under pressure until the residue in the- 15 still became too heavy for further heating with-'- out danger of coking. The next development was the Burton-Clark type of batch or semi-continuous process wherein the contents of the still were circulated through a tube heater instead of ap- 20 plying direct heat to the shell still. Then came processes of the tube or tube and drum type with "clean circulation wherein the return of' any heavy asphaltic cracked material to the heating section of the system was prevented.

25 All of these processes, however, use the principle of recycling, i. e., of recirculation of all or a substantial proportion of the insufiiciently cracked material to theheating and reaction system; Once-through processes have been pro- 30 posed, and used to a certain extent commercially,

but were'never successful on a commercial scale on account of the relatively low yield of gasoline which was possible by such processes.

I have discovered that by the use of elevated 35 temperatures and pressures, i. e., higher temperatures and pressures than those normally used in commercial cracking processes, and by the use of a selected charging stock I may eliminate substantially all recycling and nevertheless ob- 40' tain a high yield of gasoline. My particular discovery is that such a process can be operated economically on a commercial scale by separating the unconverted or insuiiiciently cracked material from the one -through reaction products 45 and cracking the majority of said unconverted materialto gases of an olefini'c character, which ,gasesare then recycled to the initial cracking step where polymerization and condensation to gasoline occurs. The operation of my process is as follows:

I utilize a selected charging stock, preferably gas oil of approximately 35 A. 1?. I. gravity which contains substantially no previously crackedtmaterial.v In the initial cracking step the fresh i5 charge is subjected to temperatures of 950 1200 F. while under pressure of 750 to 3000 lbs. per sq. in. Cracked products, which may or may not be passed through a soaking drum, go to an evaporator or separator maintained at relatively low pressure where tar and asphaltic materials 5 are eliminated. The overhead products from the evaporator are passed to a conventional bubble tower which may operate at the same or lower pressure as the evaporator and from which gasoline is eliminated as an overhead product. Heavy gas oil is eliminated from the bottom of the bubble tower but this is not cycled in the conventional' manner to the cracking step, although a part thereof may be returned to the process (subsequent to the heating system) as quenching oil. Light gas oil may be likewise eliminated from an intermediate point in the bubble tower and a part of this may be recycled to the cracking step while another part, or substantially all thereof, may be utilized as quenching oil.

The degraded gas oil, or the balance thereof, which may have a density of A. P. I., is then' passed to a high temperature low pressure cracking step wherein it is cracked substantially completely to gases and. heavy tarry or car- 25 bonaceous materials. This step may be carried out in a pipe heater or in any other suitable type of high temperature cracker. Following suitable separation steps, the olefinic gas from the high temperature low pressure cracking step 30 is recycled to the inlet of the initial high pres-' sure cracking step. Selected portions of'the gasfrom the main cracking system may be joined with the gas oil therefrom prior to the high temperature low pressure cracking step. The

high temperature cracking step is preferably operated at temperatures of 1000-1700 F. while under pressure of 0-200 lbs. per sq. in. above atmospheric.

The olefinic gases of the high temperature 40 cracking step undergo polymerization and interaction with fresh oil charged to the initial cracking step whereby greatly increased yields of gasoline are obtained, as compared with the ordinary once-through operation.

The foregoing represents a brief summary of my improved process, the full and complete de scription of which is as follows:

In the drawing attached hereto and forming a part of this specification,'Fig. 1 is a diagrammatic elevational view of suitable apparatus for carrying out my process in one embodiment thereof, and Fig. 2 is a similar view of apparatus for carrying out my process in analternative embodiment thereof. k v

- from which the stock is derived. I preferably use virgin or uncracked gas oil, i. e., a distilled fraction from crude oil containing substantially no heavy asphaltic constituents.

The charging stock after preheating by suitable heat interchange means not shown is introduced into the coils of heater wherein it is heated to temperatures of 950-1200 F. while underpressures of 750-3000 lbs. per sq. in. The time of contact in heater I l is ordinarily short, although heater |l may be provided with a soaking section.

I may also make use of an unheated soaking drum |2 following heater II. If no soaking drum is used, the heated products from heater pass directly through line i3 and valve l4 to evaporator l5, the pressure being reduced at valve l4 to the desired evaporator pressure, which in general will befrom to 250 lbs. per sq. in. I'may also introduce relatively'cool quenching oil from a suitable source (as later described) through line i6 and through valve l1, thus introducing the quenching oil just ahead of reducing valve M, or may introduce the quenching oil through valve l8 located just following valve l4.

If soaking drum I2 is used, valve I4 is closed and valves |8a and l8bare opened in which case valve |8b functions as the pressure reducing valve for bringing the pressure down to the desired evaporator pressure. In this case I may introduce. quenching oil from line l9 through valve 20 located just ahead of valve lab or through valve 2| located just subsequent to valve lab. I may also introduce all or apart of the desired quenching oil through line l6 and valve 22, which is located ahead of the soaking drum l2 whereby somewhat lower temperatures of 900l050 F. are maintained in the soaking drum II. If the soaking drum is used the hot cracked materials therefrom pass through line 23 to evaporator I5.

In evaporator I5 9. pressure of 50-250 lbs. per

sq. in. is maintained and the temperature is regulated by suitable cooling means to separate substantially all heavy tarry materials which are removed by drawoff 24. These tarry materials may be eliminated from the system, or a part thereof may be pumped by pump 25 through cooler 26 and passed into line l9 or line I6 to serve as -quenching oil as previously described, or part thereof may be passed through valve 21 in line 28 thus being returned to evaporator l5 to act as a cooling medium therein. Evaporator l5 may also be cooled by heat interchange coils with fresh charging stock orbyiother suitable means. Following evaporator |5 uncondensed vapors pass through line 29 to bubble tower 30. The pressure in bubble tower 30 may be the same as in evaporator l5 or may be regulated at some lower pressure by means. of valve 3| in line 29. The operation of bubble tower 30 is conventional. Vapors of desired light products are removed through oiftake 32 and unconverted gas oil is drawn off at the bottom of the tower through line 33. Suitable cooling means are provided which may include coils for heat interchange with fresh charging stock. The gas oil is withdrawn through line 33, and is withdrawn from the primary cracking system and utilized as later described, but a part thereof may be pumped by pump 34 through cooler and passedthrough line 35 to lines l6 or I9 to serve as quenching oil as previously described, or part may be passed through valve 31 and 31a in line 38 into evaporator |5 to serve as cooling medium therein, or may be returned through valve 39 in line 40 to serve as reflux and cooling medium in bubble tower 30.

Bubble tower 30 may also be provided with trap-out tray 4| from which light gas oil may be withdrawn through line 42. This light gas oil may be further treated as later described, but part thereof may be pumped by pump 43 through valve 44 and cooler 44b and returned to tower 30 as reflux or part may be passed through valves 45 and 45a in line 46 to pump 41 and admixed with fresh charging stock from line H] prior to entering heater I. A part of the oil from line 46 may also be passed through valve 48 and cooler 49 to lines It or I9 to serve as quenching oil as previously described. I

The vapors from bubble tower 30 are condensed in condenser 50 and passed through pressure regulating valve 5| into gas separator 52 which is ordinarily operated at essentially the same pressure as bubble tower 30 so that a relatlvely dry release gas may be separated through line 53 and eliminated from the system, or utilized, as later described. Condensed light products are removed from separator 52 through line 54 and may be withdrawn from the system through valve 55. I may, however, provide my system with a gasoline stabilizing tower in which case the condensed light products from line 54 pass through line 56 to stabilizer 51 which is provided with suitable reboiling means and reflux means whereby stabilized gasoline free from undesirable light constituents is withdrawn through bottom offtake 58 while a relatively rich stabilizer gas is eliminated overhead to line 59 and is withdrawn from the system by valve 60, or otherwise utilized as later described. I The unconverted gas oil withdrawn from bubble tower 30 through line 33 is passed through line BI. and pump 62 through low pressure high temperature heater 63. I may also pass any part of light gas oil withdrawn from tower 30 by line 42 through valve 63a and thus to heater 63.

Heater 63 is operated at temperatures of 1000- 1700 F. and pressures of 0-200 lbs. per sq. in. above atmospheric wherebythe gas oil is cracked substantially completely into gases of high olefin content plus heavy tar and carbonaceous materials. Heater 53 may be of ordinary pipe heater construction as illustrated, or may be of any other suitable construction, i. e., such as a refractory checkerwork which is alternately heated by direct combustion, etc. I may also withdraw a part of the release gas from separator 52 and line 53 through valve 64 in line 65 and introduce same by pump 66 into heater .63 in admixture with gas oil'charged thereto. I may also pass all or a part of the stablizer gas from stabilizer 51 and line 59 through valve 61 in line 68 to line 65 and pump 65 for admixture with oil charged to heater 63. If gas is admixed with oil charged to heater 63 I preferably preheat the gas by heating or heat interchange means not shown, prior to admixture with the oil whereby vaporization is promoted. This admixture of gas-with the oil charged to heater 63 not only facilitates operation of the heater by providing more complete vaporization of the charge, but also serves as an additional source of material from which gaseous olefins may be obtained.

Products from heater 63 are passed through line 69 to a suitable separator 10 which is provided with suitable cooling means, not, shown, and from which tar and carbonaceous materials are removed through drawofl II while gases and .vapors pass through line 12 to cooler 13 and materials from cooler 13 may be compressed to a suitably elevated pressure of 50-1000 lbs. per sq. in. by pump 8i. Under these conditions the gas separated in separator 15 will consist prif marily of methane and hydrogen which may be eliminated from the system through valve 82. If the light oils present in separator 15 are not suflicient in volume to efiect this scrubbing and separation of methane and hydrogen from other desired gases, I may add additional scrubbing oil (through means not shown) to separator 15 whereby this purpose is efiected. If separator 15 is operated at high pressure I remove the separated liquids through valve 83 in line 84 to stabilizer 85 which is operatedat lower pressure or higher temperature to the end that light oils free from desired gases are removed through oiltake 86while' desired olefinic gases are removed through ofitake 81. I e

The gasesproduced in heater 63 and recovered from separator 15 and/or stabilizer 85 will ordinarily have a content of gaseous olefins in excess of 35% by volume, and if separator 15 .is so operated as to eliminate substantial quantities of methane and hydrogen through vent 823 the olefin content of the total gases may be considerably higher, approaching as much as by volume. These oleflnic gases are passed through line 88 and compressor 89 and are ad! mixed with charging stock to the process in line It prior to heater Ii. Under the conditions prevailing in heater it these olefinic gases are substantially completely converted to desired products of the gasoline boiling range partly by direct polymerization and partly by complex interaction with the gas oil undergoing cracking in heater II. I may also pass a part of the stabilizer gas from stabilizer 51 through line 59, valve 61, line 68 and valve 90 to join other gasesdn line M for treatment in heater ii.

Heater ii is operated in the temperature and pressure ranges previously set forth, the rate at which oil is charged and the rate of heat input being such that at least 35% of the gas oil introduced is converted to lighter products 'of the gasoline boiling range. I prefer, however, to operate er such conditions that at least 45% of the gas oil is so converted. Due to the further conversion of the olefinic gases produced as previouslydescribed and to their interaction with the oil charging stock, the final yields of gasoline by my process will be from 65% to %,the gasoline being of high quality, in particular with respect to its antiknock quality. In addition, I achieve considerable economies in operating cost since the excessive amount of recycling per unit of fresh feed charged (which is customarily employed in present commercial processes) is eliminated thus reducing the necessary size of my equipment and eliminating excessive pumping costs.

In certain cases, depending largely on the quality and cracking characteristics of the available fresh charging stock, I may operate my procass in two once-through high pressure-high temperature stages before eliminating unconverted material and cracking same to olefinic gases for recycling. Ordinarily -I use this type of dual once-through process if the charging stock gravity is in the upper part 01' the range which I have previously disclosed as most suited for my process or, in other words, if the charging stock has a gravity of approximately 35 A. P. I, to 40 A. P. 1., although slightly lower or higher gravities may be permitted in some cases depending on the dis- ,tilla'tion range of the charging stock and on its chemical characteristics, which latter are in general determined by the crude oil from which it is obtained. In this "dual once-through modification of my process the apparatus used is essentially identical with that shown in the attached figure except that the gas oil eliminated from bubble tower 30 through lines 33 and 4-2 (except that part. thereof which may be used as quenching oil or recirculated for reflux and cooling purposes) is passed to a second high pressure-high temperature heater identical with heater H, the products from this second heater being passed into a separating system identical in function with separator i5, bubble tower 30, etc. (with or without intermediate passage through a soaking drum similar to drum ii); In this case the gas oil eliminated from the second bubble tower (except that portion thereof which may be used as quenching oil or for reflux or cooling purposes) is passed as previously de- I scribed to the low pressure-high temperature heater 63. In this case the oleiinic gases in line 88 may be pumped by pump 89 to either of the two high temperature-high pressure-heaters, or may be divided in suitable proportion between both of said heaters, in order to obtain the best balance of operating conditions and results. In this modiiication of my process the overhead system following bubble tower 30 and the analogous bubble tower of the .second stage is ordinarily combined, i. e. vapors from both bubble towers pass through a common condensing, separating and stabilizing system and the gasoline and gas-from both stages are thereby collected as single streams. In fact I may make use of one bubble tower suitably divided at its midpoint, the cracked products from each stage being introduced respectively above and below the middle dividing point, the tower being so arranged that, gasoline vapors and gas from both sections are collected in a common stream while the gas oil or unconverted material is collected in a separate stream from each section, these ,sepiau'ate streams being processed as previously described.

For example, in the practice of this dual oncethrough" of my pr Iunay use apparatus as diagratically illustrated in t 2 wherein all elements numbered from 11 to are identical with corresponding elements similarly numbered oi i.

Referring to Fig. 2, the operation of the dual once-through modification of my process is as follows: I close valve 98in line 6! and open valve $2 in line as whereby the intermediate oil M ted in bubble tower 3@ i "I through line 93 to the high pressure-high perature heater M which operates within the sametrenge of temperature pressure conditions previously described for high pressure heater ii and wherein the oil-.is subjected to relatively high conversion but ordinarily to a lower conversion than that heater II. Following heater 9| the conversion i evaporator 91 heavy residual products are withdrawn from the system through valved line IIII while vapors pass overhead through line I02 and valve I09 prior to entering bubble tower I04, which is operated similarly to bubble tower 30 previously described.- Vapors from bubbletower' I04 pass through line- I05 and join vapors produced in the first cracking step at the vapor exit from previously described bubble tower 30. Intermediate oils from bubble tower I04 are withdrawn from the bottom through line I06 and are sent by pump IIII through line I09 and valve I09 to the entrance of low pressure heater 63 previously described wherein these oils are converted to olefinic gases. after separation, etc., as previously described, may pass through valve III! in line 80 to heater II as previously described or may wholly or in part be diverted through valve III in line 2 whereby said olefinic gases are passed to the inlet of the second stage high pressure oil heater 94.

The foregoing being a full and complete description of my invention, I claim:

1. A hydrocarbon conversion process comprising subjecting relatively high-boiling hydrocarbon oil to cracking at elevated temperatures and pressures to convert a substantial portion thereof into hydrocarbons of the gasoline boiling range, separating the cracked products into tar and vapors, fractionating said vapors to recover a condensate oil heavier than gasoline and said hydrocarbons of the gasoline boiling range, subjecting said condensate oil in a separate zone to cracking at higher temperatures and relatively low pressures to convert said condensate oil primarily to normally gaseous hydrocarbons of relatively high olefinic content and heavy tarry-like material, and returning olefinic gases thus produced to the initial cracking step for conversion into normally liquid hydrocarbons in the presence of said oil.

,sion into normally liquid hydrocarbons These oleflnic gases so produced 2. A hydrocarbon conversion process comprising subjecting relatively high-boiling hfdrocarbon oil to cracking at elevated temperatures and pressures to convert a substantial portion thereof into hydrocarbons oi the gasoline boiling range, separating the cracked products into tar and vapors, fractionating said vapors to recover a condensate oil heavier than gasoline and said hydrocarbons oi the gasoline boiling range, subjecting said condensate oil in a second cracking step at elevated temperatures and pressures to convert a substantial proportion thereof to hydrocarbons of the gasoline boiling range, separating the cracked products into tar and vapors,

- Iractionating said vapors torecover a second condensate oil and said last-mentioned hydrocarbons of the gasoline boiling range, subjecting said second condensate oil in a separate zone to cracking at higher temperatures and relatively low pressures to convert said second condensate oil primarily to normally gaseous hydrocarbons of relatively high olefinic content and heavy tarrylike material, and returning olefinic gases thus produced to the initial cracking step for converin the presence of said oil.

3. A process in accordance with claim 1 wherein normally gaseous hydrocarbons are separated from the hydrocarbons ot the gasoline boiling range resulting from said first-mentioned cracking operation and at least a part of said normally gaseous hydrocarbons are admixed with said condensate oil undergoing conversion primarily to normally gaseous hydrocarbons of relatively high olefinic content and heavy tarry-like material.

4. A process in accordance with claim 1 wherein hydrogen and methane are separated from the hydrocarbons of relatively high oleflnic content prior to the return thereof to the initial cracking step.

5. A process in accordance with claim 1 wherein the relatively high-boiling hydrocarbon oil is a distillate oil containing substantially no asphaltic constituents and substantially no previously cracked constituents and is converted into at least 35% of hydrocarbons of the'gasoline boiling range in passing once through the conversion zone.

6. A process in accordance with claim 1 whereg in said condensate oil is subjected to a cracking temperature of about l000-1700 F. while under a pressure 01' about 0-200 lbs. per square inch.

FREDERICK W. SULLIVAN, JR. 

